A standard assembly of the above-described type has a plate-type heat exchanger which forms a plurality of parallel passages opening at opposite edges of the plates. Manifolds are provided at the plate edges. Liquid is pumped from the one manifold to the other through the plate passages to pick up or give off heat through the walls of of the plate unit. When used as a solar collector the plate is exposed to the sun so that the liquid picks up heat, and when used as a radiator the liquid gives off its heat to the air around the heat exchanger.
So long as such assemblies are relatively small, they are normally made as integral welded units. An upper limit to the size is normally the standard construction size of 4'.times.8'. Larger assemblies must be assembled on the job.
Accordingly it is standard practice to assembly large plate-type heat exchangers at the site. This is most easily done simply by connecting together a group of small units of the integral type described above. Such a construction results in a heat exchanger that has the high cost per unit of surface area of a small exchanger as well as a great many joints constituting potential leaks, and at the same time the ratio of effective surface area to volume is inefficiently low.
Accordingly it has been suggested to make the exchangers from separate manifold and plate units that are bolted together. Normally the plate is formed of a plurality of sections selected to give the desired total surface area, and then manifolds of appropriate length are selected. The joints between the plate edges where the passages open and the manifolds are made either by welding or bolting. Welding is obviously a difficult process that requires expert workers. Bolting, with interposition of a seal between the plate edge and the manifold, is somewhat easier, but requires relatively complicated manufacturing techniques to produce the necessary connecting holes, studs, and the like, and that has the disadvantage of occasionally producing a bad joint that must be opened up and rebuilt to stop a leak.